Gas mixture, in particular for inflating the tyres of vehicles

ABSTRACT

A gaseous composition particular suitable for inflating the tires of vehicles with a high heat transfer capacity that results in tires having a longer life and better performance. In one aspect, this composition is based on hydrofluorocarbons, and is capable of effectively conducting the heat generated during the rotation of the tire to the wheel rim and at a more or less constant pressure. In one aspect, the wheel rim acts as a radiator, exchanging the heat with the outside air, maintaining the tire temperature low and preventing it from overheating.

TECHNICAL FIELD

This invention concerns a gaseous composition particularly suited foruse in inflating the tyres of vehicles.

More in particular, this invention refers to a gaseous composition whichis designed to be used to inflate the tyres of vehicles to achieveimprovements from the point of view of performance and the overall lifeof the tyre.

This invention can be applied in the industrial sector for theproduction of non-combustible gases, and in particular in the productionof gas mixtures for the inflation of tyres.

BACKGROUND ART

It is known that the tyres of vehicles are inflated with compressed airwhich is injected into the inner chamber of the tyre through the valve,until the correct working pressure is reached.

It is also known that in the event of long road journeys especially inthe summer or in the case of extreme conditions, such as duringcompetitions with sports vehicles, the tyres tend to overheat and thepressure to increase. The hot air in the tyres tends to damage thestructure of the tyre due to oxidation and ozonolysis phenomena.

These phenomena produce dangerous and uncontrollable effects on thetyres, which after travelling a certain distance on the road or trackundergo a sudden drop in performance, with a considerable limitation inthe life of the tyres as a result of mechanical and thermo-oxidativestress.

In particular, according to the results of standard length track tests,it was found that vehicle tyres normally inflated with compressed airtraditionally undergo a sudden drop in performance after the sixth orseventh lap, continuing to decrease and making frequent gear changesnecessary.

To overcome this limitation in the performance of air-inflated tyres,the use of gas mixtures was tested and a series of gases were selectedon the basis of various properties.

The use of these gases or mixtures did not, however, lead to appreciableresults, and it was found that tyres traditionally inflated with thesenitrogen, helium or argon-based gaseous mixtures, and the tyres of tracksports vehicles, also undergo a sudden drop in performance after acertain number of laps, making it necessary to replace them after ashort time.

In fact the critical temperature for some racing tyres is 130° C., overwhich the tyre “shatters”, in other words the part which would normallybe worn out on the asphalt surface becomes detached from the pressurisedchamber.

The construction of tyres with this known technology is carried out intwo stages: the first being the pressure chamber, the second the rubbermix, which is worn out on the asphalt.

When the two parts are superimposed and vulcanised, small air bubblescould remain trapped between the two parts, and an increase intemperature over 130° C. would cause them to increase in volume finallyforming blisters that would inevitably explode.

DESCRIPTION OF THE INVENTION

This invention proposes to provide a gaseous mixture or composition thatcan be used to inflate the tyres of vehicles, thus obtainingimprovements from the point of view of performance and of the overalllife of the tyre, by controlling the temperature, thus eliminating or atleast reducing the disadvantages described above.

The invention also proposes to provide a gaseous composition that beeasily produced, thus making it economically advantageous.

This is achieved by means of a gaseous composition for the inflation ofvehicle tyres and having the features described in the main claim.

The dependent claims describe advantageous embodiments of the invention.

The gaseous composition according to the invention presents a firstfundamental feature, a high capacity of heat transfer. This is thereforea gas mixture that is able to effectively conduct the heat from therubber tyre during rotation to the wheel rim. The latter, particularlywhen made from aluminium or magnesium, acts as a radiator, exchangingthe heat with the outside air, preventing the tyre from becomingoverheated.

Thanks to the high capacity of heat transfer, tyres inflated with thisgaseous composition achieve excellent results from the point of view oftheir life, since the temperature of the tyre is kept low and thepressure is constant. This minimises damage due to oxidation andozonolysis, thus extending the life of the tyres subjected to mechanicaland thermo-oxidative stress.

These gases and mixtures according to the invention are based on gaseouscomponents whose use makes it possible to achieve the result whereby themore the speed increases the more effective the heat exchange is.

The mixture according to the invention comprises various percentages ofa series of hydrofluorocarbons.

According to an advantageous embodiment, these hydrofluorocarbonsconsist of pentafluoroethane, trifluoroethane and tetrafluoroethane.

According to a particularly advantageous embodiment of the invention,the basic mixture comprises: Pentafluoroethane HFC 125 44%Trifluoroethane HFC 143 A 52% Tetrafluoroethane HFC 134 A 4%

The mixture of these components makes it possible to obtain a baseelement called HFC R404 A.

According to another advantageous embodiment of the invention, thisgaseous mixture can be combined with a certain percentage of carbondioxide.

In this case, numerous gaseous combinations are possible; however,experiments have demonstrated a particular efficacy of the mixtureobtained according to the following composition: CO₂ 50% HFC 125 22% HFC143 A 26% HFC 134 A 2%

Numerous advantages can be obtained with the use of the mixtureaccording to the invention.

First of all, tyres inflated with this mixture have a constantperformance, and the sudden drop in performance does not occur (graph1). A certain drop in performance was, however detected, but is moregradual and above all occurs after around 11 or 12 laps.

The use of the mixture according to the invention in tyres fitted onmotorcycles keeps the pressure more or less constant, reducing thevibration phenomena which are felt above all on the front tyre(chattering effect).

The rotating mass below the shock absorbers normally has a disturbancefrequency of 15-18 Hz, while the more constant pressure achieved withthis mixture makes it possible to damp this effect, reducing it to 7-9Hz, (data taken from superimposed telemetric systems).

The working temperature also remains below the critical threshold. Whenthe mixture according to this invention is used, the temperature of thetyre never increases beyond 120° C. This is a very important factconsidering that the critical temperature for some racing tyres is 130°C., over which the tyre “shatters”, i.e. the part that is normally wornout on the asphalt becomes detached from the pressurised chamber.

The new mixture according to the invention absorbs the temperature andtransmits it to the wheel rim which acts as a radiator, keeping thetemperature of the tyre “low” by exploiting the high heat transmissioncoefficient of the gas combination which transmits and dissipates thetemperature by conduction.

With the new mixture according to the invention, the tyre is subject toless wear, the shavings are four times smaller compared to those with anair-inflated tyre and after a race a mixture-inflated tyre loses halfthe weight compared to an air-inflated tyre.

Thanks to the use of the mixture according to the invention, it willalso be possible to manufacture softer tyres, improving the “grip” andthe consequent lap time for competition vehicles, guaranteeing the teama better performance with respect to other tyre manufacturers.

DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become evident onreading the following description of one embodiment of the invention,given as a non-binding example, with the help of the enclosed drawing,in which FIG. 1 is a graph representing the performance of tyres inrelation to the laps covered on a standard length track in the twoconditions of inflation with air and with the gas mixture.

DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

The gaseous composition according to the invention suitable to be usedto inflate vehicle tyres consists of a mixture of hydrofluorocarbons.

In particular, according to a particularly advantageous embodiment, thiscomposition comprises a basic component named HFC R404A consisting of:Pentafluoroethane HFC 125 44% Trifluoroethane HFC 143 A 52%Tetrafluoroethane HFC 134 A 4%

Advantageously, the use of this gaseous mixture can be combined with acertain percentage of carbon dioxide, according to the followingpreferred composition: CO₂ 50% HFC 125 22% HFC 143 A 26% HFC 134 A 2%

Basically, the gaseous mixtures obtained consist of hydrofluorocarbonsand more in general of gases characterised by their high capacity ofstoring cold heat as well as having a high heat transfer coefficient.

The achieved effects of the mixtures refer mainly to a more constanttemperature of the inflated tyres, a more constant pressure and thepossibility of using softer mixes, and consequently providing bettertrack performance.

First of all, tyres inflated with this mixtures have a constantperformance, with no sudden drop, as can be seen in the diagram in FIG.1.

As this diagram shows, a certain drop in performance was noted, but thisis more gradual and above all it occurs after around 11 or 12 laps.

The table below indicates the data relative to the behaviour of tyresinflated with various gas mixtures and subjected in an artificialenvironment to temperature and pressure tests on the basis of the testtime measured in minutes.

The tests were carried out only on rear tyres since they are moresubject to temperature problems.

During the tests the tyres were rotated for a period of time at acertain speed; the speed was then increased until the tyres burst.

The tests were accordingly carried out by rotating the tyres on asurface with a load of 162 kg at an ambient temperature of 25° C. and atincreasing speeds: for the first 20 minutes at 115 kmph and forsubsequent intervals of 10 minutes at increasing speeds from 230 to over300 kmph.

The first column in the table indicates the various mixtures used in thetwo rear tyres.

The second column indicates the temperatures of the tyres after 60minutes of testing and the third column the tyre pressure after 60minutes.

The fourth column indicates the temperature values when the tyre bustsand the fifth the time in minutes after which the tyre burst, while thesixth and last column shows the pressure in bars at the time ofbursting.

As can be seen, the mixture giving the best performance is the oneindicated in the seventh and the eleventh line, consisting of 50% of 404and 50% of CO₂.

The results measured with the use of this high-performance mixtureindicated the longest times at tyre bursting, i.e. 103 and 117 minutes,which are higher than all the other values.

At the end of the test period, the high-performance mixture made itpossible to increase performance by 22.1%, and the tyres burst at a muchhigher speed, this result being achieved by a lowering of thetemperature according to the essential features of the new mixture, andby maintaining the pressure at the inflation values. Tyre Temp- TyrePressure after Tyre Bursting Tyre Life before Tyre Bursting Gas Typeafter 60 min (° C.) 60 min (bar) Temp. (° C.) Bursting (min) pressure(bar) Nitrogen Tyre 1 91 33 3.25 Nitrogen Tyre 2 101 3.27 128 64 3.30Helium Tyre 1 125 55 3.25 Helium Tyre 2 103 3.15 108 65 3.16 CO₂ Tyre 194 3.09 136 76 3.11 CO₂ Tyre 2 111 3.10 135 71 3.15 507 Tyre 1 96 3.20132 89 3.25 507 Tyre 2 88 3.18 91 3.20 404 Tyre 1 92 3.30 119 78 3.34404 Tyre 2 81 3.25 124 95 3.35 134 Tyre 1 99 3.16 114 70 3.22 134 Tyre 292 3.20 112 70 3.21 404 50% 85 3.00 119 103 3.05 CO₂ 50% 404 75% 93 3.15149 101 3.25 CO₂ 25% 507 50% 91 3.27 157 98 3.35 CO₂ 50% 507 75% 95 3.27120 94′ 3.35 CO₂ 25% 404 50% 91 3.15 148 117 3.29 CO₂ 50% 137 404 25% 933.10 137 102 3.18 CO₂ 75%

Once the most suitable mixture had been found, the tyres were analysedto check whether the mixture could have damaged the elastomer or itscomponents in any way.

The perfect integrity of the elastomer and its main components wasconfirmed and, thanks to solid state high resolution NMR spectroscopy,the various samples inflated with the various gases and mixtures werecompared. These tests confirmed that the sample inflated with thehigh-performance mixture gave the best results, minimising the damagedue to oxidation and ozonolysis, extending the life of the tyressubjected to mechanical and thermo-oxidative stress.

The gas mixture according to the invention can be used in the tyres ofairplanes, trucks, articulated trucks, buses, cars or other vehicles,with greater performance in terms of life, rotating silence and lowerfuel consumption due to the more stable conditions inside the chamber,all in total safety since the mixture is completely inert. Especiallyfor heavy vehicles, this means that in the event of a tyre catchingfire, as a result of its bursting and of the high temperature, the gaswould extinguish the fire.

As can be seen, this gas mixture makes it possible to achieve all theresults described above, including above all those relative to the factthat the tyres inflated with this mixture give a constant performanceand the traditional sudden drop in performance does not occur.

The invention is described above with reference to a preferredembodiment.

It is nevertheless clear that the invention is susceptible to numerousvariations, within the framework of technical equivalents.

1. A gas mixture, in particular for inflating the tires of vehicles,comprising: a mixture with a high heat transfer capacity.
 2. A gasmixture suitable for injection to inflate the tires of vehicles of claim1, wherein said mixture comprises hydrofluorocarbon-based compositions.3. A gas mixture of claim 2, wherein said hydrofluorocarbon-basedcomposition comprises a percentage of pentafluoroethane HFC
 125. 4. Agas mixture of claim 2, wherein said hydrofluorocarbon-based compositioncomprises a percentage of trifluoroethane HFC 143A.
 5. A gas mixture ofclaim 2, wherein said hydrofluorocarbon-based composition comprises apercentage of tetrafluoroethane HFC 134A.
 6. A gas mixture of claim 3,wherein said hydrofluorocarbon-based composition comprises: 44% ofPentafluoroethane HFC 125; 52% of Trifluoroethane HFC 143A; and 4% ofTetrafluoroethane HFC 134A, to obtain a basic mixture called HFC 404A.7. A gas mixture of claim 2 further comprising: a percentage of carbondioxide.
 8. A gas mixture of claim 7, wherein said percentage of carbondioxide is around 50%.
 9. A gas mixture of claim 8, further comprising:22% of HFC 125 Pentafluoroethane, 26% of HFC 143A Trifluoroethane, and2% of HFC 134A Tetrafluoroethane.
 10. A gas mixture of claim 2, whereinsaid hydrofluorocarbon-based composition comprises a percentage oftrifluoroethane HFC 143A.
 11. A gas mixture of claim 3, wherein saidhydrofluorocarbon-based composition comprises a percentage oftetrafluoroethane HFC 134A.
 12. A gas mixture of claim 4, wherein saidhydrofluorocarbon-based composition comprises a percentage oftetrafluoroethane HFC 134A.
 13. A gas mixture of claim 3 furthercomprising: a percentage of carbon dioxide.
 14. A gas mixture of claim 4further comprising: a percentage of carbon dioxide.
 15. A gas mixture ofclaim 5 further comprising: a percentage of carbon dioxide.